Safety Features for Medical Devices Requiring Assistance and Supervision

ABSTRACT

An automatic locking system for a medical treatment device helps to ensure that an assistant is present during treatment of a patient. Among the features disclosed biometric authentication to verify that a trained assistant is present, a presence detector to ensure the assistant is continuously present during treatment, and warning and recovery processes that allow intermittent lapses in the continuous presence of the assistant.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent application Ser. No. 14/682,440, filed Apr. 9, 2015, which is a continuation of U.S. patent application Ser. No. 13/618,716, filed Sep. 14, 2012, now U.S. Pat. No. 9,024,746, issued May 5, 2015, which is a continuation of U.S. patent application Ser. No. 12/091,728, filed Aug. 19, 2008, now abandoned, which is a national stage entry of International Application No. PCT/US2006/060218, filed Oc. 25, 2006, which claims the benefit of priority of U.S. Provisional Patent Application No. 60/596,840, filed Oc. 25, 2005, all of which are incorporated herein by reference in their entireties.

BACKGROUND

Home treatment can provide tremendous benefits for sufferers of chronic ailments such as renal failure. But there is potential for harm in the home setting that is offset in a clinical setting by the presence of trained staff. If a patient undergoing dialysis, for example, has a reaction due to unforeseen conditions, the staff can take immediate action to assist the patient, even if the patient loses consciousness. In the home, this role may be played by a trained assistant. The instructions and training associated with home use may be replete with admonitions against attempting to perform a treatment without following the requirement that the assistant be in attendance, but there is always a need for creative approaches that further help to ensure that such requirements are fulfilled.

SUMMARY

A home treatment system includes various devices to limit the potential for a patient to misuse a home medical treatment device or its components by limiting access to or use of equipment while not attended by an assistant or other authorized party.

According to an embodiment, a method verifies proper use of a medical device. The method includes authenticating an authorized person other than a patient to be treated using a device attached to a treatment device used to treat the patient, generating an enabling signal to cause the treatment device to become operable in response to a result of the step of authenticating, verifying at least one time during a treatment interval that an individual other than the patient is at a treatment location where the patient and the treatment device are located, performing a warning procedure responsively to a result of the step of verifying. The warning procedure includes generating a signal to indicate an impending termination of treatment within a specified time. The method further includes waiting for the individual to verify a presence of the individual within the specified time and terminating a treatment of the patient responsively to and after the step of waiting.

In a further embodiment, the authenticating includes machine-recognizing a biometric indicator of identity. The warning procedure may include displaying requirements for a treatment procedure, a message requesting the presence of the authorized person, a message transmission to a remote terminal such as a cell phone, a remote networked terminal (such as at a medical center), or a land line telephone. The authenticating may include reading a magnetic medium storing a data key, a finger, retina, keypad entry, RFID tag, the receiving of a mechanical key, or any suitable authentication process.

In a particular embodiment, the authenticating includes machine-classification of a video image such as recognizing the face of an assistant. Video classification is particularly useful in this context because it allows the treatment scene to be assessed in a variety of ways. For example, a video scene can be classified to determine if a person other than the patient remains with the patient during the treatment. The video system can “watch” the scene to make sure that if the helper does leave for a period of time, it is only for a predefined interval. A model of the treatment scene can be predefined as part of the classification process. For example, the model may specify that the helper will prepare a meal at a particular time or that the helper uses the bathroom with a predefined frequency. Thus, the model may be identified as storing a “pattern of presences of the helper.” The model can be programmed specifically for this purpose or it can be acquired passively by observing behavior. By comparing consistency with the model (or in the case of the passively acquired model, this amounts to consistency from treatment to treatment) the video recognition system can determine if the non-presence of a helper is out of an expected bound. For example, if the model indicates that the helper should leave approximately at noon for 15 minutes and the helper leaves for 30 minutes, the system may initiate the protective features described in this application, such as sounding an annunciator or displaying a message to try to call back the helper or, upon failing that, the system may go into a failsafe mode. A video system even can have the ability to determine if the helper has fallen asleep by observing posture and movement of the helper.

Preferably, the method further includes authenticating an authorized person at least three times during a treatment interval, the three times being spaced apart such that the third time is more than half-way through the treatment interval. Even more preferably, the system continuously monitors indicia of the presence of the helper.

A medical device, comprising: controls for operating the medical device; a lock that prevents at least some functions of medical device from being operable through the controls; the lock granting initial access to the medical when a key is applied to the lock; a message generator that indicates that the medical device will go into a failsafe mode unless the lock is applied again at at least one time during a treatment interval; the lock permitting continued operation of the in response to the key being applied at the at least one time; the medical device being configured to go into the failsafe mode when the key is not applied during the at least one time.

The lock may be configured to perform machine-recognition of a biometric indicator of identity. The device may include a display and a message generator that displays on the display requirements for a treatment procedure. The device may also have a communication device including one of a wireless terminal, a telephone, and a networked terminal that generates a message indicating the failure of the key to be applied to the lock at the at least one time. The key may include a magnetic medium storing a data key. The lock may include a video camera and a device configured for machine-classification of a video image from the video camera. The lock may be a simple structure, for example one that prevent access by locking an access panel covering the controls.

Note that here and elsewhere in the specification, the term “video image” can also refer to a video stream or sequence of images or a metric derived from it. For example, an activity level in a scene can be determined from a compression metric such as MPEG motion compensation vector, or the average total energy in the motion compensation vector over a period of time. This would also fall under the meaning of “video image.”

According to another embodiment, a medical device, has a medical treatment component and a monitoring system configured to receive data from sensors to confirm the presence of a helper. The helper is different from a patient receiving treatment by the medical treatment component. The monitoring system is configured to confirm a pattern of presences of the helper during a treatment period in which the medical treatment component is operative to deliver therapy to a patient. The monitoring system generates a signal indicative of an abnormal condition when the pattern of presences of the helper is not confirmed.

The monitoring system can include a video camera and a video classification engine that monitors a scene that includes a patient and a helper. In this embodiment, the monitoring system may initially authenticate the helper using any of a variety of known techniques, such as fingerprint identification. This process may also include machine—classification of a video image such as recognizing the face of the helper. Video classification is particularly useful in this context because it allows the treatment scene to be assessed in a variety of ways and continually monitored. For example, a video scene can be classified to determine if a person other than the patient remains with the patient during the treatment. The video system can “watch” the scene to make sure that if the helper does leave for a period of time, it is only for a predefined interval. A model of the treatment scene can be predefined as part of the classification process. For example, the model may specify that the helper will prepare a meal at a particular time or that the helper uses the bathroom with a predefined frequency. Thus, the model may be identified as storing a “pattern of presences of the helper.” The model can be programmed specifically for this purpose or it can be acquired passively by observing behavior. By comparing consistency with the model (or in the case of the passively acquired model this amounts to consistency from treatment to treatment) the video recognition system can determine if the non-presence of a helper is out of an expected bound. For example, if the model indicates that the helper should leave approximately at noon for 15 minutes and the helper leaves for 30 minutes, the system may initiate the protective features described in this application, such as sounding an annunciator or displaying a message to try to call back the helper or, upon failing that, the system may go into a failsafe mode. A video system even can have the ability to determine if the helper has fallen asleep by observing posture and movement of the helper.

The sensors in this embodiment, instead of being a video camera (or in addition to a video camera and recognition engine) can also include components that are much simpler such as a pressure sensor in a chair or a proximity sensor which responds to the presence of the helper near or on the sensor. The sensor may be a keypad the prompts the helper to enter a code that indicates that helper is present and there are no problems with the treatment. The ability of the keypad entry to be made confirms the helper is available. Preferably, the helper would know the keycode for entry into the keypad but the patient would not. In this way the presence of the helper can be confirmed quite simply.

The authentication device or the presence indicator or sensor may include at least one of a key code receiver, an RFID reader, a mechanical lock, a biometric reader, a mag stripe reader, a non-volatile memory card reader, a smart card reader, a video camera, or a bar code reader. The monitoring system may go into a failsafe mode in response to the abnormal condition signal. The monitoring system may cause the medical treatment component to go into a failsafe mode in response to the abnormal condition signal. The monitoring system can generate an alert signal in response to the abnormal condition signal. It may wait for the reception of an alert-cancel command after generating the alert signal in which case it would reset and continue normal treatment operation of the medical treatment component. But if the alert-cancel command was not received, the monitoring system would cause the medical treatment component to go into a failsafe mode.

The failsafe mode of the present and other embodiments may include clamping blood lines and/or sending remote alerts such as a phone call to an ambulance service or 24 hour medical treatment facility. It may include the slowing of the blood pumping rate. The failsafe mode may be any operational mode that reduces the risk to the patient for any of the problems that can arise in a treatment. In a preferred embodiment, the features described in the present patent specification are applied to a renal replacement therapy system and/or a extracorporeal blood treatment.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A is an illustration of an interface environment that supports various inventive embodiments.

FIG. 1B illustrates an embodiment of a locking cabinet used to store components used for treatment.

FIG. 2 is a flow chart illustrating a use case including human behavioral and state machine state changes.

FIG. 3 is a flow chart illustrating an embodiment for controlling access or use of equipment or components for home medical treatment.

FIG. 4 is a flow chart illustrating a further embodiment for controlling access or use of equipment or components for home medical treatment.

FIG. 5 is a flow chart illustrating a further embodiment for controlling access or use of equipment or components for home medical treatment.

FIG. 6 is a flowchart illustrating a further embodiment for controlling access or use of equipment or components for home medical treatment.

DETAILED DESCRIPTION OF THE FIGURES

Referring to FIG. 1A, a medical device 10 may have a controller 2 that controls the functions of the medical device 10. Examples of medical device 10 include renal replacement therapy, infusion pumps and associated systems; medical monitoring equipment, medicating systems, exercise equipment, physical therapy equipment, pulmonary treatment devices such as for chronic obstructive pulmonary disease, oxygen delivery systems, cardiac treatment or monitoring devices, and many others that may be evident to those of ordinary skill based on the current disclosure.

The medical device 10 may have a movable or stationary locking or lockable part 40 that is susceptible to locking or effects a locked and/or unlocked state. For example, it may be a part that is locked or a device, such as an actuator, that actually effects locking. Examples include solenoids, simple mechanical locks, software state machines with locked states through which operational flow is blocked, and other equivalent devices.

The controller 2 may implement a locking function or the entire medical device 10 may be susceptible to locking. Examples of a lockable part 30 include an access panel, hatch, door or other mechanical security component or mechanical interface such as a slot for receiving consumable components; a component controller, power supply, or a crucial component such as a pump or other prime mover; a user interface or component interface. The lockable part 40 may or may not be physically attached to the medical device 10. Its operative relationship with the medical device 10 and other elements, however, will become clearer from the greater disclosure.

The Medical device 10 may have one or more of a variety of communications and input and output elements, including:

A wireless terminal 70 to communicate with remote wireless terminals 75 such as cell phones, email devices, telemetry systems, wireless computer terminals, and similar devices. The medical device 10 may, for example, transmit information and receive commands via such devices.

An imaging device 35 such as a charge coupled device (CCD) video camera, laser scanner such as an industrial photometric scanner, an infrared camera, terahertz wave (T-wave) shortwave, acoustic, or other kind of imaging device. The medical device 10 may employ video image processing and recognition techniques to identify faces, determine the number of individuals present in a room, patient body surface temperature profile, or myriad other functions using the one or more imaging devices represented by imaging device 35.

A wired terminal 85 such as a plain old telephone (POT), annunciator such as an audible or visual alarm, intercom, or similar device. The medical device 10 may employ the wired terminal 85 to notify local or remote personnel of status or change of status at a treatment site. For example, the device 10 may place an automatic phone call to emergency medical personnel if predefined conditions ate detected. The medical device 10 may also report attempts to authorize a treatment (see further below for discussion of this) or an attempt to use the medical device 10 to an authorized party with supervisory obligations.

The treatment device 10 (or a component thereof) may be connected to a network or the Internet 54 to communicate with information servers 55 and/or remote terminals 80. The medical device may use this capability to obtain instructions from the server 56, to report status or notify of conditions requiring special or immediate attention, and similar transactions. The medical device 10 may also use such communication modes to report attempts to authorize a treatment (see further below for discussion of this) or an attempt to use the medical device 10 to an authorized party with supervisory obligations.

A direct input/output (I/O) interface 15 such as a keyboard, keypad, speech interface, digital display, touchscreen, touchpad, or other I/O device and mechanical interface such as levers, buttons, knobs, etc. One or more such devices may be used to allow users or others to command and control the medical device 10 and/or the controller 2.

A connector 25 such as a port (e.g., USB port), mechanical keyhole, smart card reader, bar-code reader, mag-stripe reader, RFID reader, biometric sensor, handwriting recognition interface, or other interface device, which may be used for authorizing and/or authenticating a user and/or assistant.

A key or identification indicator represented figuratively at 20. These may include a human finger (fingerprint), retina, face, or other biometric indicator; an electronic key such as a magnetic stripe, radio frequency identification device (RFID) unit, nonvolatile memory (NV memory), bar code or other data carrier; mechanical key; or any device used in a remote or local authorization or authentication process. Another example is a key fob with a password or digital key embedded in a memory and a USB connector on it.

The above examples are by no means intended as an exhaustive list and are considered to encompass their equivalents and additional examples within the identified categories.

In an alternative embodiment, shown in FIG. 1B, a locker 55 is provided to contain components that are used with the medical device 50 such that their inaccessibility reduces the ability of someone without access to the locker 55 to harm himself or another. Cloud 70 is intended to represent any or more of the input and output elements discussed and illustrated with reference to FIG. 1A. An example of the use of the locker would be as a store to hold consumables such as needle accesses or disposable blood circuits without which the medical device 50 could not be employed. The embodiment of FIG. 1B has the additional benefit of mitigating any risks from harm from the locked-up components themselves with or without the medical device 50. In the embodiment of FIG. 1B, the locker 55 may include substantially the same I/O Interface and/or connector 25 as discussed with reference to FIG. 1A.

Referring now to FIG. 2. the medical device 10, 50, &/or associated component(s) such as locker 55, indicated collectively at M, may be equipped as illustrated in the previous figures to perform the functions (use cases) indicated in FIG. 2. In embodiments, there are three individuals who may be involved: a patient 1; an assistant who is trained to monitor and also, possibly assist the patient 1 in using the medical device or associated component(s) M; and a supervisor, such as a medical doctor who has some responsibility with regard to the use of the medical device &/or associated component(s) M. The assistant 2 may be trained to provide emergency treatment or help in the set up of the equipment. In the ease of renal replacement therapy or chemotherapy, there may be a potential for serious adverse reactions including loss of consciousness. In embodiments, the assistant 2 would be present at a site where the medical device 10, 50 is used. The supervisor 3 may be charged with ensuring that a strict protocol is followed, such as a doctor, or may just be a second assistant. The supervisor may be at the site or remote from it.

A function A may be to prevent access by the patient 1 without the assistant 2 being present. In embodiments, the assistant 2 carries a key or, inherently, a biometric identifier such as his/her face. If the assistant 2 is not present, the medical device &/or associated component(s) M may be equipped, as discussed above, to deny access to the medical device &/or associated component(s) M. This prevents the patient 1 from using the medical device &/or associated component(s) M without assistance.

Another function B may be to check external conditions such as a time of day when use of the medical device &/or associated component(s) M is permitted or scheduled. This may provide an additional layer of protection against misuse. The medical device &/or associated component(s) M may check the external conditions, such as time of day, whether the assistant's training is current or expired, whether a prescription has been provided, or other separate criterion beyond the presence of the assistant. The presence of the assistance may be verified by another function C which is an authentication function. In the latter, the assistant may present his/her key or other indicia of identity and presence to unlock the medical device &/or associated component(s) M for use.

Another function D is to permit access to the medical device &/or associated component(s) M and, depending on the embodiment, including receiving and executing commands for control and setup as well as administering treatment or other service. Another function E is to provide services by the medical device &/or associated component(s) M.

Any improper use or proper attempt, to use the medical device &/or associated component(s) M may be reported by a function F to supervisor 3. For example, if the medical device &/or associated component(s) M detects a failure of authentication, it may report the event to the supervisor 3. The medical device &/or associated component(s) M may report every attempt, whether proper or improper, to the supervisor 3, and may also report to the assistant 2. In the latter case, if an authentication function C is executed without the assistant 2 being present, the assistant 2 may be notified by a communication to a remote terminal such as a cell phone. The latter situation could arise if the assistant 2 lost his/her key.

Note that the above use cases are not comprehensive nor is each function essential. Some benefits may be provided by a mechanically-locking cabinet configured to house the medical device &/or associated component(s) M, where the key is retained by the assistant. Another simple alternative for the medical device is for it to have a locking component.

Referring now to FIG. 3, in a process that may be implemented by an attached controller (including controller 2) medical device 10 (50 or locker 55) may be disabled or rendered inaccessible respectively at step S10. Step 10 may represent a default condition. The disabling of the medical device may be provided through locking or lockable part 40. In step S15 an unlock event is detected, such as the entry of an authorization procedure implemented through a programmable processor in controller 2 or an attempt to connect smart card or memory device (embodiments of key/ID indicator 20). Here a user may be attempting to use the medical device 10 or 50 or access locker 55. If there is no unlock event at S15, then control returns to step S10. If there is, then an authorization process is performed at step S20. The authorization process may include verifying biometric indicia of identify, reading a smart card or other device including any of the devices identified with key/ID indicator 20.

Physically, what's going on so far in the process of FIG. 3 is that someone is attempting to gain access to the locker 55 or the medical device 10 or 50 to use it or obtain contents. In a preferred embodiment, the medical device or locker 10/50/55 is located at a patient's home and an assistant keeps the key/ID indicator 20 with him or her such that the patient cannot gain such access by him or herself. When the assistant or other authorized party is present, the assistant may complete the authorization process S20 and generate a valid condition (yes) at step S25.

In step S25, the validation process may verify that the key or identification indicia are present. This provide evidence that the assistant or authorized party is present such that access may be provided (to medical device 10, 50 or locker 55) in step S30. If a valid authorization is not completed in step S25, a failure action may be taken such as the display of a message on the user interface of the medical device or locker 10/50/55 or an output on any of the other I/O devices shown in FIGS. 1 and 2, such as a wireless message to a remote supervising party. The process may loop through step S35 until a treatment or other medical operation is performed, as appropriate, permitting the medical device 10/50 to returned to the default state S10. The latter step will loop through step S15 until an attempt is made to access supplies or equipment.

Step S20 may include using any type of key/ID indicator 20 or any action using I/O interface 15. For example, a username and/or password may be entered using the I/O interface 15 or a mechanical key may be used to unlock the lockable part 40, Also, step S30 may include enhancing services that are available through the medical device &/or associated component(s) M rather than simply enabling or disabling access. Step S40 may provide for remote notification such as an automated email or cell phone message. It may also include permanent logging of failures to authorize access.

Referring now to FIG. 4, two steps may be added to the procedure of FIG. 3 to check for the maintenance of a predefined status. For example, the predefined status may be that the assistant must remain, at least between intervals, present at the use location of the medical device &/or associated component(s) M. At step S50, it is determined if the status is not being maintained. If it is being maintained, control loops through step S50 until it is not. Then a correction procedure may be implemented at step S55 and if the status is recovered, control returns to step S50. If not, the medical device &/or associated component(s) M may be disabled or ameliorative response may be generated or automatically requested (not shown as a separate step) by the medical device &/or associated component(s) M.

Step S50 may correspond to one or more of the following, which are shown to provide illustrative examples and not to limit the embodiments in any way:

Prompting at predefined intervals through I/O interface 15 for confirmation of identity and presence of the assistant 2 by entering a password or voice command (with voice biometric identification).

Prompting at predefined intervals through I/O interface 15 for confirmation of identity and presence of assistant 2 by connecting a key/ID indicator 20.

Classifying a scene taken in by imaging device 35 to determine if the assistant 2 is still present, taking appropriate actions. Support for known techniques for this and other video classification concepts are shown in U.S. Pat. No. 6,611,206 for “Automatic system for monitoring independent person requiring occasional assistance;” U.S. Pat. No. 7,028,269 for “Multi-modal video target acquisition and re-direction system and method;” U.S. Pat. No. 6,931,596 for “Automatic positioning of display depending upon the viewer's location;” U.S. Pat. No. 6,925,197 for “Method and system for name-face/voice-role association;” U.S. Pat. No. 6,778,705 for “Classification of objects through model ensembles;” U.S. Pat. No. 6,714,594 for “Video content detection method and system leveraging data-compression constructs;” U.S. Pat. No. 5,561,718 for “Classifying faces;” U.S. Pat. No. 7,110,569 for “Video based detection of fall-down and other events; ” U.S. Pat. No. 7,110,570 for “Application of human facial features recognition to automobile security and convenience;” US Application Publication Nos. 20060210112 for “Behavior recognition system;” 20060210958 for “Gesture training;” 20060204050 for “Face authenticating apparatus and entrance and exit management apparatus;” 20030128126 for “Method and apparatus for error warning with multiple alarm levels and types” and 20030128125 for “Method and apparatus for machine error detection by combining multiple sensor inputs” all of which are hereby incorporated by reference as if fully set forth in its entirety herein. (Note: The latter two applications describe mechanisms for observing a patient for safety reasons and illustrate a context in which video is captured of a treatment scene. This context is similar to what is described presently in the context of confirming the presence of the patient's helper. That is, these applications illustrate how a camera may be positioned to acquire the scene including a patient and a helper. They also illustrate response mechanism that may be used with the present embodiments.)

Classifying a scene taken in by imaging device 35 to determine the status of the patient, for example, if the patient's body temperature profile has changed to a predetermined pattern indicating imminent loss of consciousness, lack of blood flow or a pathological condition such as rapid or slow breathing. Support for known techniques for this may also be found in the above reference.

Step S55 may correspond to one or more of the following, which are shown to provide illustrative examples and not to limit the embodiments in any way:

Generating a wireless message or automated cell phone call to the assistant 2.

Generating a wireless message or automated cell phone call to the supervisor 3.

Generating an alarm.

Changing the operational regime of the medical device 10, 50 to a safe mode.

Note that step S60 may include returning the medical device 10, 50 to a normal operating mode. If the operating mode is changed, or performing a function to disable an alarm or respond to a message.

Referring now to FIG. 5, a step S120 is added to the flow of FIG. 3 for verifying some external condition in addition to the authentication process. This may be for example, checking that the current time and date are correct for use of the medical device &/or associated component(s) M. It may include checking an internally stored prescription for currency. It may include checking the status of the training or training level of the assistant. The latter may include checking a database stored on the server 56 which stores the assistant's identification in relation to training level and comparing to a predefined protocol also stored on the server 56.

Referring to FIG. 6, a step S150 may be added which includes generating a notification, such as by cell phone, email, instant message, SMS message, POT call, or other means to notify the assistant that his or her key is being used to authenticate in step S20. For example, if the assistant lost his/her key, the notification would provide the assistant the ability to take some action if the assistant were not actually present. Step S125 may include waiting for an additional time for an action to be taken in response to the step of S150.

Although the present invention has been described herein with reference to a specific preferred embodiment, many modifications and variations therein will be readily occurring to those skilled in the art. Accordingly, all such variations and modifications are included within the intended scope of the present invention as defined by the following claims. 

1. A medical device, comprising: a medical treatment component; a monitoring system configured to receive data from sensors to confirm the status of a patient or a helper, where the patient receiving treatment by the medical treatment component and the helper is a different person from the patient; the monitoring system including a video camera positioned to view a scene containing a helper or a patient; and a controller programmed to implement an image classification engine to process video images from the video camera during a time when the medical treatment component is operative to deliver therapy to a patient; the controller being programmed to classify said processed video images to identify specific conditions and generate a signal indicative of an abnormal condition in response thereto.
 2. The device of claim 1, wherein one of the specific conditions includes a presence or non-presence of a helper.
 3. The device of claim 1, wherein one of the specific conditions includes a pattern of presences or non-presences of a helper over a period of time.
 4. The device of claim 1 wherein one of the specific conditions includes a predetermined body temperature profile pattern.
 5. The device of claim 1 wherein one of the specific conditions includes a patient breathing rate.
 6. The device of claim 1 wherein one of the specific conditions includes a pathological condition of a patient.
 7. The device of claim 1 wherein one of the specific conditions includes a helper falling asleep.
 8. The device of claim 1, wherein the controller is programmed to create a cell phone message in response to said signal.
 9. The device of claim 1, wherein the controller is programmed to an alarm in response to said signal.
 10. The device of claim 1, wherein the controller is programmed to recognize a face of the helper.
 11. The device of claim 10, wherein the controller is programmed to prevent use of the medical treatment component responsively to failing to recognize a face of a helper.
 12. The device of claim 3, wherein the pattern of presences is determined by a stored schedule based on time of day. 